During the manufacture of printed circuit boards, metal foil stencils are used to deposit solder. The metal stencil serves as a mask over which a blade is used to squeegee solder through stencil holes onto conducting pads of the circuit board. A variety of background information about stencils can be found in U.S. Pat. Nos. 4,486,466; 4,893,403; 4,789,096; 4,976,813; 5,359,928; 5,493,075; 5,746,127; 5,800,856; 5,825,639; 5,984,166; 6,267,818; 6,273,327; 7,190,157; 7,220,975; 7,412,923; all of which are hereby incorporated by reference.
A typical stencil is very delicate. Stencils often range from between about 1.5 and 8 mils of thickness—and sometimes more and sometimes less. Many are made of stainless steel or a nickel alloy. Because stencils are so thin, they are very delicate and very easily damaged. Many stencils are framed to facilitate handling and mounting of the stencil without damaging the stencil. Other stencils are frameless and flexible, and can be rolled up like a street map.
A typical stencil—being custom made for a particular circuit board design—is also very expensive. Many cost thousands of dollars. To create the stencil, a laser is programmed to cut thousands of small, precisely-placed apertures to serve as the stencil holes. Each circuit board may require hundreds or thousands of solder points; and each stencil may be applied as a mask to multiple circuit boards simultaneously.
Even a minor dent, crease, or impression (commonly referred to as a “coin”) in the stencil can result in circuit board defects. Manufacturers frequently suffer significant losses scrapping their coined stencils and idling manufacturing lines while waiting for replacement stencils to be fabricated, shipped, and installed.
Before this invention there was no process, known to the applicant, for repairing coined metal stencils. Rather, the normal practice in the industry is to simply dispose of the damaged stencils. Accordingly, there is a need for a method of repairing coins in stencils, in order to minimize the need to replace these expensive stencils and the losses associated with lengthy production line shutdowns.